Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.53   9.677%   $68.581   $68.58   $68.60   $68.60  
  Purchase #2 $5.35   11.620%   $5.9717   $5.97   $5.95   $6.00  
  Purchase #3 $198.64   10.549%   $219.5945   $219.59   $219.60   $219.60  
  Purchase #4 $174.82   7.533%   $187.9892   $187.99   $188.00   $188.00  
  Purchase #5 $202.35   5.691%   $213.8657   $213.87   $213.85   $213.90  
  Purchase #6 $227.78   12.842%   $257.0315   $257.03   $257.05   $257.00  
  Purchase #7 $66.41   6.436%   $70.6841   $70.68   $70.70   $70.70  
  7 purchase totals = $937.88       $1,023.7177   $1,023.71   $1,023.75   $1,023.80